Preparation of 17alpha-ethynylestriol

ABSTRACT

mide to yield a mixture of isomers having the following structures:   wherein R&#39;&#39;&#39;&#39; is H, C1-C3 alkyl or C5-C6 cycloalkyl; reacting the 16 Alpha ,17 Alpha -dihydroxy isomer with acetone in the presence of acid to yield a compound of the formula   wherein R&#39;&#39;&#39;&#39; has the same meaning as hereinabove; separating said acetonide from the desired 16 Alpha ,17 Beta -dihydroxy isomer, and recovering said 16 Alpha ,17 Beta -dihydroxy isomer substantially free from any 16 Alpha ,17 Alpha isomer.

United States Patent Bach et al.

PREPARATION OF 17ALPHA- ETHYNYLESTRIOL Inventors: Nicholas J. Bach; Eugene Farkas, both of Indianapolis, Ind.

Assignee: Eli Lilly and Company, Indianapolis,

Ind.

Filed: March 24, 1971 Appl. No.: 127,771

[451 Oct. 10, 1972 Primary Examiner-Henry A. French Attorney-James L. Rowe and Everet F. Smith [57] ABSTRACT An improved process for preparing l7a-ethynylestriol utilizing a novel isomer separation process 2 Claims, No Drawings PREPARATION OF 17ALPHA-ETHYNYLESTRIOL BACKGROUND OF THE INVENTION l7a-Ethynylestriol and its 1 7B-ethynyl-l 7a-hydroxy isomer are disclosed by Engelfried, et al., Arzneim. Forsch. 16, 1518-21 (1966). As disclosed in the copending application of Kraay and Farkas, Ser. No. 127,690, filed this even date, l7a-ethynylestriol is a weak estrogenic hormone but its 3-cyclopentyl ether is an extremely potent estrogen having a favorable uterotropic-vaginal ratio in its hormonal action. The 3- cyclopentyl ether derivative of l7a-ethynylestriol can be prepared either by reacting a metal salt of 17aethynylestriol (as prepared by Engelfried et al., supra.) with cyclopentyl bromide or by ethynylating the 3- cyclopentyl ether of l6a-acetoxyestrone. The latter procedure gives a preponderance of the undesired 17B- ethynyl-l7a-hydroxy isomer. By contrast, ethynylation of l6a-acetoxyestrone itself yields a preponderance of the desired 17a-ethynyl-17a-hydroxy isomer, which upon etherification yields the more potent hormone isomer. The chief drawback of this latter procedure, however, is the lack of a satisfactory method of separating the two isomeric estriol products produced by the ethynylation reaction.

It is an object of this invention to provide a rapid, efficient procedure for separating 17a-ethynylestriol from its 17/3-ethynyll 7a-hydroxy isomer.

SUMMARY In fulfillment of the above and other objects, this invention provides a process for separating 17aethynylestriol from 1 7B-ethynylestra-l ,3 ,5( 10)-triene- 3,l6a,l7a-triol (its 17B-ethynyl-17a-hydroxy isomer) which comprises the formation of an acetonide of the latter compound followed by separation of the acetonide from the unreacted 16a,17B-dihydroxy compound by chromatography, fractional crystallization or other suitable method. The above process is operative not only for compounds having a free phenolic group at the 3 position of the estriol molecule but also for those compounds having a lower alkyl or cycloalkyl ether group in the 3 position. Our novel process is illustrated III 11+ l Acetone CECH OH;

CHa

wherein R is H, C C, alkanoyl, C -C alkyl or C -C cycloalkyl, R is C -C alkyl, and R" is H, C -C alkyl or C -C cycloalkyl.

In the above formula, R can be n-butyryl, isobutyryl, propionyl, acetyl, formyl, methyl, ethyl, n-propyl, isopropyl, cyclopentyl, cyclohexyl, or the like group, and R can be methyl, ethyl, n-propyl, or isopropyl.

l7a-Ethynylestriol (Reaction Scheme l;R"=H) can be converted into its 3-cyclopentyl ether by reaction with a cyclopentyl halide in the presence of sodium methoxide, thallium ethylate, or like base. As set forth in Ser. No. 127,690, filed this even date, 17aethynylestriol 3-cyclopentyl ether is particularly useful in treating menopausal syndrome. All of the compounds, however, coming within the scope of formula 1] above, and prepared in pure form by the process of this invention, have an estrogenic action with a favorable uterotropic-vaginal ratio.

This invention is further illustrated by the following specific example:

EXAMPLE A 3 molar ethyl magnesium bromide Grignard Reagent in tetrahydrofuran, prepared according to standard procedures, was filtered through glass wool and added slowly to 700 ml. of tetrahydrofuran previously saturated with acetylene at about 0C. During the addition of the ethyl magnesium bromide, the reaction mixture was cooled to about 0C. and in addition, acetylene was slowly bubbled through the solution. The resulting reaction producedabout 1.75 moles of ethynyl magnesium bromide in 1,300 ml. of tetrahydrofuran. Next, a solution containing 10 g. of l6a-hydroxyestrone diacetate [prepared by the method of Leeds, Fukushima, and Gallagher, J. Am. Chem. Soc. 76, 2943 (1954)]in 250 ml. of tetrahydrofuran was added to the ethynyl magnesium bromide solution in dropwise fashion. The reaction mixture was refluxed for 24 hours under a nitrogen atmosphere and was then cooled to about 0C. About 750 ml. of a saturated ammonium chloride solution was added carefully, followed by an equal volume of water. The organic materials were extracted into ethyl acetate. The ethyl acetate layer was separated and washed successively with water and saturated aqueous sodium chloride. The solution was dried and the solvents were evaporated in vacuo. The resulting residue was triturated with about 1 l. of boiling hexane and the hexane extract discarded. The remaining insoluble material was dissolved in about 1,500 ml. of acetone to which was added 5 ml. of percent aqueous perchloric acid. The solution was transferred to a flask which was stirred magnetically at ambient temperatures for about 12 hours. An excess of solid sodium bicarbonate was added and the resulting mixture filtered. The filtrate was concentrated to a volume of about 250 ml. and diluted with an equal volume of ethyl acetate. The ethyl acetate layer was washed successively with water and saturated aqueous sodium chloride and was dried. The volatile constituents were removed by evaporation in vacuo. The resulting residue was slurried with chloroform and chromatographed over about 500 g. of florisil. Elution with 3,000 ml of chloroform, followed by evaporation of the chloroform in vacuo, yielded an orange oil. The oil was dissolved in an ether-hexane solvent mixture to yield crystals of l7B-ethynylestral ,3 ,5( l)-triene-3, 1 6a, 1 7 a-triol-l6,l7-acetonide, melting at about 208-2l 1 C. (The 17B-ethynyll 7a-hydroxy isomer is produced as a minorcomponent in the reaction of 16a-hydroxyestrone diacetate and ethynyl magnesium bromide.) Further development of the chromatogram with 1,000 ml. of ether gave a fraction containing both 17aethynylestriol and the 173 isomer, as determined by thin layer chromatography. Finally, elution with 1 l. of methanol yielded, after evaporation of the solvent, a dark brown solid showing only a single spot in thinlayer chromatography. The solid was washed with chloroform and filteredto yield about g. of 17aethynylestriol asa light tan powdery solid melting with decomposition at about 243245 C. Recrystallization of the solid from an ethyl acetate-hexane mixture yielded light tan crystals of 17a-ethynylestriol melting with decomposition at about 245 C.

l 1.3 g. of 17a-ethynylestriol thus produced were dissolved in 500 ml. of methanol. A 50 percent molar excess of freshly prepared sodium methoxide in methanol was added. The resulting solution was concentrated in vacuo to a solid comprising the sodium salt of 17aethynylestriol. The solid was dissolved with warming in 500 ml. of dimethylformamide. 50 ml. of cyclopentyl bromide were added and the mixture heated to reflux under. a nitrogen atmosphere for about 4 hours. The reaction mixture was cooled and then diluted with l l. of ethyl acetate and l l. of water. The resulting organic layer was washed three times with water followed by saturated aqueous sodium chloride wash and was then dried. Evaporation of the solvent in vacuo yielded a solid residue which was slurried with chloroform-and chromatographed over about 100 g. of florisil. Elution with chloroform.yielded a brownish solid residue on evaporation of the solvent. Recrystallization of this residue from a mixture of ethyl ether and hexane yielded about 7.7 g. of 17a-ethynylestriol 3-cyclopentyl ether, melting at about l62-l 65 C.

An alternative preparation for the last step of the procedure is as follows: 2.1 g. of l7o'z-ethynylestriol were dissolved in 100 ml. of absolute ethanol. A solution containing about 0.6 ml. of thallium ethylate in ml. of benzene was added with stirring in dropwise fashion. Stirring was continued for another 10 minutes after which time the solvents were removed by evaporation in vacuo. The residue, comprising the thallium salt of l7a-ethynylestriol, was slurried with 100 ml. of dimethylformamide. 10 ml. of cyclopentyl bromide were added and the mixture heated at 90-95 C. for 4 hours under a nitrogen atmosphere. 17a- Ethynylestriol 3cyclopentyl ether thus produced was isolated and purified as in the above example.

In accordance with the above procedure, 16ahydroxyestrone, 3-methyl ether l6-acetate and 16ahydroxyestrone 3-cyclopentyl ether l6-acetate. can be reacted with ethynyl magnesium bromide to yield mixtures of l7B-ethynylestral ,3,5( l0)-triene-3, 1 6a, 1 7atriol 3-methyl ether and l7a-ethynylestriol 3-methyl ether and l 7B-ethynylestral ,3,5( 10)-triene-3, 1 6a, l7a-triol 3-cyclopentyl ether and 17a-ethynylestriol 3- cyclopentyl ether, respectively. In each instance the undesired 1601,1711 derivative is converted to the acetonide according to the above procedure and the acetonide separated from the unreacted l6a,l7B isomer, the desired isomers, by chromatography, thus yielding purified l7a-ethynylestratriol 3-methyl ether and l7a-ethynylestratriol 3-cyclopentyl ether. 7

Other compounds which can be prepared in substantially pure form free from their 17a-hydroxy isomers include:

l7a-ethynylestn'ol 3-cyclohexyl ether,

l7a-ethynylestriol 3-ethyl ether, and

l7a-ethynylestriol 3-isopropyl ether.

We claim:

1. The process which comprises reacting a compound of the structure wherein R is H, C -C alkanoyl, C -C alkyl or C -C cycloalkyl; and R is C -C alkyl; with ethynyl magnesium bromide to yield a mixture of isomers having the following structures:

wherein R" is H, C C alkyl or C -C reacting the l6a,l 7a-dihydroxy isomer with acetone in the presence of acid to yield a compound of the formu- CECE CH3 3,697,558 5 6 wherein R has the same meaning as hereinabove; 2. The process of obtaining l7a-ethynylestratriol separating said acetonide from the desired 16a,l7[3- f ee rom an impurity comprising its l7B-ethynyl-l,3,5 dihydroxy isomer, and recovering said 1601,1713- i which dihydroxy isomer substantially free from any 16a,l7a prises forming an acetoniqe of F' i Y Q Y isomen 5 isomer and then separating said acetomde impurity from said l7a-ethynylestratriol by chromatography. 

2. The process of obtaining 17 Alpha -ethynylestratriol free from an impurity comprising its 17 Beta -ethynyl-1,3,5(10)-estratriene-3,16 Alpha ,17 Alpha -triol isomer, which comprIses forming an acetonide of said 16 Alpha ,17 Alpha -dihydroxy isomer and then separating said acetonide impurity from said 17 Alpha -ethynylestratriol by chromatography. 